Advanced composites are high strength, high modulus materials which are finding increasing use as structural components in aircraft, automotive, and sporting goods applications. Typically they comprise structural fibers such as carbon fibers in the form of woven cloth or continuous filaments embedded in a thermosetting resin matrix.
Most advanced composites are fabricated from prepreg, a ready-to-mold sheet of reinforcement impregnated with uncured or partially cured resin. Resin systems containing an epoxide resin and aromatic amine hardener are often used in prepreg since they possess the balance of properties required for this composite fabrication process. State-of-the-art epoxy/carbon fiber composites have high compressive strengths, good fatigue characteristics, and low shrinkage during cure. However, since most epoxy formulations used in prepreg are brittle, these composites have poor impact resistance and tensile properties which do not fully translate the properties of the reinforcing fiber. Thus, there is a need for resin systems which afford composites with improved tensile and impact properties.
In the prior art, there are two references to the attempted toughening of epoxy resin systems by adding thermoplastic polymers. These were not successful. Specifically, polyethersulfone modification of a tetraglycidyl methylene dianiline/4,4'-diaminodiphenyl sulfone did not improve toughness (British Polymer Journal, 15, pages 71 to 75; Proceedings of the 28th National SAMPE Synposium, April 12 to 14, 1983, pages 367 to 373).